The present invention relates to an electric horn of a motor vehicle, and particularly to a controlling method and apparatus of constant-frequency sound production for the electric horn. This invention also relates to a method for producing a signal source which has constant-frequency and continuous, adjustable duty cycles.
Nowadays, the basic sound-production theory for an electric horn of a motor vehicle is that the horn uses an electromagnget to drive a diaphragm, which then pushes the air and produces sound. The attractions of the electromagnet in that kind of horns are controlled by a contact. When the horn works, since the contact is operating at a very high frequency (generally 300-600 Hz), the on-off of the large electric current may generate a big spark. The corrosion of the contact caused by the electric spark makes the horn short life and at the same time continuously makes it deviate from the standard frequency and sound level both of which are set when the horn is off the production line. It brings about some disadvantages such as sound variations, sound reduction, and noise increase. Furthermore, it is very difficult to make the sounding frequency consistent with the inherent mechanical resonant point (frequency) of the horn to achieve the maximum sounding efficiency and maximum energy savings. In recent years with the developments of the electronic technology, various kinds of electronic devices have been invented to replace the contact, wherein an electric circuit instead of the contact is used to generate pulse currents (signals) for the electromagnet to drive the diaphragm. However, since they are adjusted in accordance with the inherent mechanical resonant point of each horn individually, all the electronic devices are constituted by circuits with their frequencies adjusted via resistors and capacitors, such as various kinds of multi-harmonic oscillators, time-base circuits, pulse width adjusting and controlling circuits. Since this kind of circuit is influenced by temperature and voltage features of semiconductor devices and resistors and capacitors, its output frequency being influenced by the environmental temperature and the motor vehicle""s voltage, it can not be kept stably at the frequency consistent with the inherent mechanical resonant frequency of the horn. Therefore, although the above said horn has a longer life than the horns with a contact, it still has some disadvantages For example, the variations of the environmental temperature and the motor vehicle""s voltage result in changes of the driving frequency of the circuit which finally cause the frequency of the horn sound to change and the output sound level greatly reduce. So far it has not been used widely.
A quartz crystal oscillator or a highly stable oscillator within some semiconductor chips has high stability of frequency, generally up to several dozens of PPM, but it can only generate a frequency of 2-1/N when using ordinary frequency dividing method. However, the inherent mechanical resonant frequency of a horn is at a frequency point between 300 and 600 HZ, therefore these general frequency dividing methods can""t be used here. Although frequency division can be effected by a digital voltage controlled oscillator (VCO), it exists a problem that the pulse width can not be arbitrarily adjusted. So it is not applicable to be used in a horn for its too high cost relative to a horn and its complicated adjusting method.
An object of the invention is, with respect to the problems in the prior art, to design and provide a method and apparatus which uses a constant-frequency oscillator such as a quartz crystal oscillator to generate a stabilized reference signal, then via a monolithic-processor controls the reference signal, corrects its frequency according to the inherent acoustic parameters of each horn to generate a driving signal, and then makes the horn to achieve the optimum sounding effect when driven by the generated electronic driving signal, thereby overcomes the problems such as the sound variations (frequency variations) and unstable output sound level which are not solved in the prior art.
According to the first aspect of this invention, there is provided a control method of constant-frequency sound production for an electric horn, the above said method includes the following steps: generating a reference pulse signal of a constant frequency; pre-dividing the reference pulse signal generated by the generating step into a predetermined level which is near a certain frequency at the work frequency range of the horn; correcting the frequency of the pulse signal generated in the step of pre-dividing based on the predetermined frequency parameters of the horn so as for the frequency of output pulse signal to be consistent with the said certain frequency; adjusting the duty cycle of the frequency-corrected pulse signal based on the predetermined duty cycle parameters so as for the horn to achieve the optimum sounding characteristics; buffering and power-amplifying the signal output from the duty cycle correcting unit; then sending the buffered and amplified pulse signal into the electric horn to drive the electric horn to work.
In the above first aspect of this invention, the said certain frequency in the frequency correcting step is the mechanical resonant frequency of the electric horn.
According to the second aspect of this invention, there is provided a controlling method of constant-frequency sound production for an electric horn by microprocessor, the said method includes the following steps: generating a reference pulse signal of constant frequency; according to the predetermined frequency parameters of the horn and the predetermined duty cycle parameters, simultaneously adjusting the frequency and the duty cycle of the generated reference pulse signal using the microprocessor so that the pulse signal generated subsequently has a predetermined frequency and duty cycle, wherein the said predetermined frequency which is very near the mechanical resonant frequency and in the electric horn""s working frequency range, the predetermined duty cycle is enough for the horn to achieve the optimum sounding characteristics; buffering and power amplifying the signal output from the adjusting step; then sending the buffered and amplified frequency signal into the electric horn so as to drive the electric horn to work.
According to the third aspect of this invention, there is provided an control apparatus of constant-frequency sound production for an electric horn, the said apparatus includes: a reference signal generating unit for generating a reference pulse signal of constant frequency; a pre-dividing unit for pre-dividing the reference signal generated by the reference signal generating unit into a predetermined level which is near a frequency in the working frequency range of the electric horn; a frequency correcting unit for correcting the frequency of the pulse signal generated in the pre-dividing unit based on the predetermined frequency parameters of the horn so that the output pulse signal frequency is consistent with a certain frequency within the working frequency range of the electric horn""s diaphragm; a duty cycle adjusting unit for adjusting the duty cycle of the frequency-corrected pulse signal based on the predetermined duty cycle parameters so as for the horn to achieve the optimum sounding characteristics; a buffering and amplifying unit for buffering and power amplifying of the signal output from the duty cycle correcting unit; then sending the buffered and amplified pulse signal into the electric horn to drive the electric horn to work.
In the said apparatus in the above third aspect of this invention, the said pre-dividing unit, the said frequency correcting unit and the said duty cycle adjusting unit may be implemented by a monolithic-processor, and also may be constituted by a microprocessor or a which includes CPUL, I/O, RAM, ROM (EPROM, EEPROM, FLASH or other devices having similar memory function) or other similar devices. Furthermore, in the case that the monolithic-processor circuit""s normal. work is not affected, the horn according to the invention can used as a horn having variable sound level by changing the apparatus""s supply voltage and thus controlling the output sound level of the electric horn.
According to the forth aspect of this invention, there is provided a method generating a signal source having constant frequency and adjustable duty cycle using a microprocessor, the said method includes the following steps: generating a reference pulse signal of constant frequency; pre-dividing the reference pulse signal generated in the step of generating reference signal so as for the pre-divided pulse signal frequency to fall into a predetermined working frequency range; correcting the frequency of the pulse signal generated in the step of pre-dividing based on the predetermined working frequency so as for the output pulse signal frequency to be consistent with the required work frequency; adjusting the duty cycle of the frequency-corrected pulse signal based oil the predetermined duty cycle.
In the forth aspect of this invention, the adjusting range of the said duty cycle in said method of generating signal source may be 1%-99%.
Compared with the prior art, this invention has the following advantages:
1. In this invention, a constant-frequency oscillator (such as quartz crystal) is used to generate a constant reference pulse signal, a monolithic-processor is adopted to control the pulse signal via software programs to generate a special signal, the frequency of which is consistent with the horn""s full-band sounding characteristics and the special pulse width of which is generated by software programs, then make a correction based on the data of each horn in a memory, amplify and sequentially drive the electromagnetic diaphragm of the horn to sound. It resolves the problems existing in common methods which can""t arbitrarily divide the frequency of signals output by constant-frequency oscillator (such as quartz crystal oscillator). And also it has some advantages over the digital voltage controlled oscillator (VCO), the VCO may resolve the problem of frequency division, but it can""t resolve the problem of adjusting the pulse width arbitrarily, in the meantime the cost of VCO is too high relative to a horn, therefore VCO is not suitable to be used in the horn.
2. The horn according to the invention has a long life, and overcomes the shortages existing in a conventional horn with a contact, such as sound variations and volume reduction when its frequency and sound level continuously deviate from the standard values set at the time of being off the production line, therefore the maximum sounding efficiency and electricity savings may be achieved. At the same time, it also overcomes the weaknesses that when an electronic device is used to replace the contact the changing of output frequency influenced by the environmental temperature and voltage of a motor vehicle leads to sound variations and output sound reductions.
3. This invention can serve several purposes. Besides being used as a given motor vehicle""s electric horn which is driven by a signal having constant frequency and adjustable duty cycle, the apparatus according to the invention, even in the case that the voltage supplied by motor vehicle changes greatly, can keep a constant frequency output signal and only the output sound level is changed correspondingly, for example, a constant-frequency electric horn having a 12V nominal voltage and sounding under the control of a monolithic-processor can work stably at a range of 6.5xcx9c16V, thereby resolving the problems that can""t be resolved by various horns in the prior art in which its diaphragm is driven by an electromagnet. Since the frequency of its output signal is unrelated to voltage and the sound level of the output signal varies corresponding to the variations of the input voltage, it can be used as a sound-level-variable horn by changing the input voltage. Sounding with a lower sound level is preferred in a city in order to reduce the environmental pollution, and sounding with its higher sound level may be used in a noisy environment in order to ensure the traffic safety. Furthermore, it can be used as a signal source, with both the frequency and pulse width adjustable.